1. Field of the Invention
The invention pertains to the field of variable cam timing. More particularly, the invention pertains to a method of using a variable camshaft timing device with a hydraulic lock in an intermediate position for automatic restarts of a stop start mode of an engine and cold restarts of the vehicle.
2. Description of Related Art
By reducing the idling time of an internal combustion engine in a vehicle, the fuel efficiency is increased and emissions are reduced. Therefore, vehicles can use a “stop-start mode” which automatically stops and automatically restarts the internal combustion engine to reduce the amount of time the engine spends idling when the vehicle is stopped, for example at a stop light or in traffic. This stopping of the engine is different than a “key-off” position or manual stop via deactivation of the ignition switch in which the user of the vehicle shuts the engine down or puts the car in park and shuts the vehicle off. In “stop-start mode”, the engine stops as the vehicle is stopped, then automatically restarts in a manner that is nearly undetectable to the user of the vehicle. In the past, vehicles have been designed primarily with cold starts in mind, since that is the most common situation. In a stop-start system, because the engine had been running until the automatic shutdown, the automatic restart occurs when the engine is in a hot state. It has long been known that “hot starts” are sometimes a problem because the engine settings necessary for the usual cold start—for example, a particular valve timing position—are inappropriate to a warm engine.
Most engines with a phaser place the phaser in the retard position on engine shutdown using a lock pin or a series of lock pins, in preparation for the next start.
As an example, U.S. Pat. No. 5,924,395 is a patent for variable cam timing in a stop-start engine control system. When a stop signal is detected by the ECU, the intake valves are changed to the most retarded position in preparation for an upcoming hot start. In one embodiment in the '395 patent, a lock pin fixes the vane of the phaser in the most retarded position by inserting a lock pin into a retard-side engagement hole.